1. Field
The described technology relates generally to a silicon crystallization system and a silicon crystallization method using a laser, and more particularly, to a silicon crystallization system and a silicon crystallization method that are capable of improving energy uniformity in a longer-axis direction of a laser beam.
2. Description of the Related Art
A liquid crystal display (LCD) and an organic light emitting diode (OLED) display, which are types of flat panel display devices, can be fabricated to be thin and light, so they are commonly used as a display device for mobile electronic devices, and their application coverage is extending to large-scale display devices. In particular, as the necessity for a display device requiring high speed operational characteristics emerges, research for such a display device is actively ongoing.
In order to satisfy the high speed operational characteristics of a display device, a channel region of a thin film transistor (TFT) must be formed by using polycrystalline silicon instead of amorphous silicon that has electrical mobility of about 0.1 cm2/Vsec to 0.2 cm2/Vsec. Polycrystalline silicon has electrical mobility of about 20 cm2/Vsec to 150 cm2/Vsec, thereby implementing a faster operational speed compared with amorphous silicon.
An annealing method using a laser is one of conventional methods for forming polycrystalline silicon. The annealing method involves irradiating a high energy laser beam onto an amorphous silicon thin film deposited on a glass substrate. Upon receiving the laser beam, the amorphous silicon thin film is melted by the heat and then solidified so as to be crystallized. This method is advantageous in that the glass substrate is not damaged by the heat.
In the laser crystallization method, an energy distribution of an output laser beam, which generally has a Gaussian distribution, is changed by using an optical system. That is, in order to enhance uniformity and productivity of crystallization, the output laser beam is transformed into a linear laser beam, which is longer in one direction.
In order to create the linear laser beam by changing the energy distribution of the output laser beam, a homogenizer is employed. An optical system using the homogenizer serves to divide a laser beam in particular directions by a homogenizer array and make the respective divided layer beams overlap on the same plane, to thereby make the energy distribution of the laser beam more uniform.
In this respect, however, compared with a case where the divided laser beams overlap in an area that is narrower than the initial laser beam, when the laser beams overlap in an area that is larger than the initial laser beam, the energy uniformity of the laser beam is low due to factors such as the optical characteristics of the laser, a defect of the optical system, and the like.
In addition, as flat panel display devices increase in size, the length of the laser beam in the longer-axis direction needs to be longer to enhance productivity of the flat panel display devices. This inevitably results in degradation of the energy uniformity in the longer-axis direction of the laser beam.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.